Projectile boattails

ABSTRACT

An aerodynamically stable projectile comprising a substantially cylindrical main body portion and a boattailed base portion having a rear face of substantially equilateral polygonal configuration, with three or more inwardly slanted surfaces. The slanted surfaces may be contiguous or non-contiguous; when they are non-contiguous, the non-slanted tail portions of the projectile form fin-like shapes.

v United States Patent 1191 1111 3,873,048

P1310 Mar. 25, 1975 PROJECTILE BOATTAILS l,l78,5l6 4/1916 Hardcastle 102 9211 3,401,637 9/1968 Briscoe 244/31 X [751 Amie" Flam", 3.434.425 3/1969 Critcher.... 102/921 [73] Assignee: The United States of America as represented by the Secretary of the Primary Examiner-Robert Slab] Army, Washington, DC, Attorney, Agent, or Firm-Robert P. Gibson; 1 Filed: Nov. 1973 Theodore Ma or; Nathan Edelberg {21] Appl. No.: 418,799 [57] ABSTRACT An aerodynamically stable projectile comprising a [52] US. Cl 244/3.l, 102/921, 244/33 tantially Cylindrical main body portion and a boat- [51] Int. Cl. F42b 11/02 ta l d as portion having a r ar a of substantially [58] Field of Search 244/3.1, 3.3; 102/921, equilateral po yg configuration. with three or 102/922, 92.3, 92.4, 92,6, 38, 56 more inwardly slanted surfaces. The slanted surfaces may be contiguous or non-contiguous; when they are [56] References Cited non-contiguous, the non-slanted tail portions of the UNITED STATES PATENTS projectile form fin-like shapes.

179,054 6/1876 Pollard lO2/92.1 5 Claims, 8 Drawing Figures PROJECTILE BOATTAILS STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION It is customary to streamline a projectile by tapering its base to a frustoconical configuration. to reduce aerodynamic drag. Such a tapered projectile base is customarily referred to as a boattail. A conventionally boat-tailed projectile is subject to substantial deflection in flight when rotating around its longitudinal axis, due to the well known Magnus force or Magnus effect. Attempts to counteract the Magnus force have been made by providing tail fins, but they are costly and create difficult design and manufacturing problems.

SUMMARY OF THE INVENTION l have found that the Magnus effect on a rotating projectile in flight can be mininized by providing the projectile with a boattail base of substantially polygonal configuration. That is, the rear face of the projectile base is contoured as an equilateral polygon of three or more sides, e.g., three to six sides, preferably three or four. While equilateral polygons with more than six sides are not excluded from the scope of my invention, they are less efficient stabilizers than polygons with up to six sides, because the more sides a polygon has, the more it approaches the configuration of a circle.

In addition to the aerodynamic advantages of projectiles in accordance with my invention, there is the important advantage of ease and cheapness of manufacture. especially as compared with the high cost of producing conventionally finned projectiles.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which illustrate several exemplary embodiments of my invention diagramatically (not scale):

FIG. I is a side elevational view of a projectile in accordance with my invention, having a three-sided boattail;

FIG. 2 is an end view corresponding to FIG. 1;

FIG. 3 is a side elevational view of a projectile in accordance with my invention, having a four-sided boattail;

FIG. 4 is an end view corresponding to FIG. 3;

FIG. 5 is a side elevational view of a modified projectile in accordance with my invention having a threesided boattail and integrally formed tail fins;

FIG. 6 is an end view corresponding to FIG. 5;

FIG. 7 is a side elevational view of still another modified version of a projectile in accordance with my invention. having a finned boattail with three canted sides; and

FIG. 8 is an end view corresponding to FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show the simplest embodiment of an aerodynamically stable projectile according to my invention. The projectile 11 comprises a generally cylindrical main body 12 of circular cross-section, having a conventional ogival nose 13 and a novel boattailed base portion 14. The base portion 14 is defined by a rear face in the form of an equilateral triangle 15 inscribed in a circle commensurate with a circular cross-section through the main body 12 of the projectile, and by three equidistant identical slanted surfaces or planes 16, 17, 18 bounded by curves whose vertices lie in an imaginary circle 19, positioned on the cylindrical surface I2 of the projectile body.

A conventional rotating band or bourrelet (not shown) is advantageously provided on the cylindrical body of the projectile forwardly of 19, for providing spin rotation to the projectile.

In the illustrated embodiment, the plane surfaces 16, l7, l8 are slanted at about 7; however, this slant angle may be varied substantially depending on the projectile caliber and other design variables; e.g., at about 5to 9.

The interior of the projectile, as shown, is hollowed out at 20, in accordance with conventional ammunition manufacturing techniques.

The slanted surfaces in the rear of the projectile have a stabilizing effect when the projectile spins during flight, and provide aerodynamic lift which conteracts the destablizing Magnus effect, by setting up a reverseacting Magnus force in rotating flight.

A similar projectile 21 having. a generally cylindrical main body 22 is shown in FIGS. 3 and 4; however, the boattailed base portion 23 is formed by a square rear face 24 and four slanted surfaces or planes 25, 26, 27, 28. The operation and the aerodynamic principles of this square boattailed projectile are similar to those of the above-discussed triangular boattailed projectile of FIGS. 1 and 2.

Other analogous embodiments, such as pentagonal or hexagonal boattails (not shown) are also within the purview of my invention, but are presently less preferred.

In the modified embodiment of my invention illustrated in FIGS. 5 and 6, additional aerodynamic lift is obtained in rotary spin flight of projectile 3l,.by providing a boattail 32 of three (or more) slanted surfaces or planes 33, 34, 35 bounded by U-curves of lesser maximum width than in the embodiment of FIGS. I and 2; these surfaces are non-contiguous, thus leaving fin-like portions 36, 37, 38 between'them, with shoulders 39 terminating at the rear face 40 of the projectile.

In a still further modified version of my invention, as shown in FIGS. 7 and 8, a projectile 41 is provided with an aerodynamically stabilized boattail 42 of three (or more) surfaces 43, 44, 45, which are both longitudinally slanted and laterally canted at a compound angle relative to the longitudinal axis of the projectile. This configuration provides the additional benefit of reducing the roll-damping movement of the boattail, when the projectile is rotating (spinning) in flight. As shown in FIGS. 7 and 8, the compound angle illustrated is about 7"; however, this value may be substantially varied, as indicated above. By suitably limiting the maximums widths of boattail surfaces 43, 44, 45, fin like portions 46, 47, 48 are preferably formed in a manner analogous to that of the embodiment shown in FIGS. 5 and 6, and confer a similar advantageous aerodynamically stabilizing effect on the projectile while in spin flight.

'fipia eaiiies'ar the present iaveiinaa'msy be "of suitable material such as steel or other heavy metal and may be produced by conventional manufacturing techniques such as forging and machining. The projectiles may be incorporated into cartridge cases of conventional designs for ammunition for artillery and infantry weapons, or may be combined with molded propellants of the caseless ammunition type.

Other variations and modifications of my invention will readily occur to those skilled in the art, and are thus to be considered to fall within the scope of the following claims.

I claim:

1. An aerodynamic-ally stable projectile comprising an ogival nose. a substantially cylindrical main body portion and a boattailed base portion formed by at least three equidistant identical slanted surfaces, each said slanted surfaces originating at a point on the cylindrical surface of said main body and each of said slanted sur faces being terminated by a straight side at the rear face of said base portion. said straight sides being noncontiguous to each other thereby forming fin-like portions between said slanted surfaces, and wherein the cross-section of each of said fin-like portions tapers outwardly from a minimum cross-sectional dimension at its minimum radial distance from the centerline of the projectile to a maximum cross-sectional demension at its maximum radial distance from the projectile centerline.

2. A projectile according to claim 1, having three said slanted surfaces.

3. A projectile according to claim 1, wherein said straight sides form a regular polygon at said rear face.

4. A projectile according to claim 3, having three said fin-like portions.

5. A projectile according to claim 3, wherein said slanted surfaces are laterally canted.

=l =l =l 

1. An aerodynamically stable projectile comprising an ogival nose, a substantially cylindrical main body portion and a boattailed base portion formed by at least three equiDistant identical slanted surfaces, each said slanted surfaces originating at a point on the cylindrical surface of said main body and each of said slanted surfaces being terminated by a straight side at the rear face of said base portion, said straight sides being non-contiguous to each other thereby forming fin-like portions between said slanted surfaces, and wherein the cross-section of each of said fin-like portions tapers outwardly from a minimum cross-sectional dimension at its minimum radial distance from the centerline of the projectile to a maximum cross-sectional demension at its maximum radial distance from the projectile centerline.
 2. A projectile according to claim 1, having three said slanted surfaces.
 3. A projectile according to claim 1, wherein said straight sides form a regular polygon at said rear face.
 4. A projectile according to claim 3, having three said fin-like portions.
 5. A projectile according to claim 3, wherein said slanted surfaces are laterally canted. 